|Publication number||US7596381 B2|
|Application number||US 10/641,526|
|Publication date||Sep 29, 2009|
|Filing date||Aug 15, 2003|
|Priority date||Aug 15, 2003|
|Also published as||EP1507428A1, US20050037778|
|Publication number||10641526, 641526, US 7596381 B2, US 7596381B2, US-B2-7596381, US7596381 B2, US7596381B2|
|Inventors||Sarvar M. Patel|
|Original Assignee||Alcatel-Lucent Usa Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Non-Patent Citations (3), Classifications (6), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
This invention relates generally to telecommunications, and, more particularly, to wireless communication systems.
2. Description of the Related Art
As will be appreciated, the communication between a base station and a mobile station 12 has great potential for interfering with the communication between another base station and another mobile station 12. This potential interference exists for base stations in the same network as well as between base stations in different networks. Also, communication between a single base station and two different mobile stations 12 has the potential for interfering with one another. To avoid this interference, wireless communication systems such as Code Division Multiple Access 2000 (CDMA 2000) wireless systems use codes to differentiate transmissions. As will be described below, base stations BSs use codes generated from different offset values to differentiate between transmissions by different base stations. Also, a base station BS uses codes to differentiate between different traffic channels assigned to mobile stations 12 by the base station BS.
In a CDMA 2000 system, each service provider assigns an identifier BS_ID to the base stations to uniquely identify each base station in the network. However, a base station identifier BS_ID does not necessarily uniquely identify base stations in different networks. When transmitting, a base station codes its transmission based on a different offset such as the pseudoNoise (PN) offset in CDMA 2000. In CDMA 2000, the PN offset is a 9-bit string that differentiates one base station BS from its neighboring base stations even when those base stations are in different networks. As illustrated in
When a base station assigns a traffic channel over which the mobile station 12 may communicate, the base station uses codes to differentiate one traffic channel transmission from another traffic channel transmission. In CDMA 2000, a different Walsh code is used to code each traffic channel of a base station. As with the PN offset, the Walsh code assigned to a traffic channel between the base station and a mobile station 12 is communicated to the mobile station 12 in a message over a forward control channel. At the mobile station 12, the mobile station 12 decodes the transmission over the traffic channel and differentiates one traffic channel from another using the Walsh code.
Codes are also used to differentiate reverse link transmissions (mobile station to base station) over traffic channels. The code used by a mobile station to code and differentiate traffic channel transmissions is referred to as a code mask. In a CDMA 2000 system, the code mask is referred to as the long code mask, and two types of long code masks are known: private and public. In a CDMA 2000 system, the public long code mask (PLCM) is typically formed using the electronic serial number (ESN) of the mobile station 12. The PLCM in a CDMA 2000 system is 42-bits long; however, other long code mask sizes exist. Typically, the PLCM includes a plurality of bits for indicating the type of the long code mask (private or public), along with a 32-bit ESN of the mobile station 12. The 32-bit ESN is often considered the variable portion of the PLCM.
For the base station to decode the traffic channel transmission for the mobile station 12, the base station needs to obtain the mobile station's ESN, and numerous methods are known in the art for accomplishing this. As an alternative to the above-discussed PLCM generation method, a CDMA 2000 system also provides that the base station BS may assign a PLCM of its choosing to a mobile station 12 during a call activation (e.g., call origination or call delivery).
Owing to the large and growing number of mobile stations 12, the supply of 32-bit ESNs is being exhausted, and discussions have begun on transitioning from the use of 32-bit ESNs to 56-bit mobile equipment identifiers (MEIDs). The use of a 56-bit MEID poses several challenges in the context of generating public long code masks. Directly using a 56-bit MEID value (for a PLCM that is otherwise 42-bits long) would require hardware changes. Accordingly, several proposals exist for using the MEID to generate the public long code mask that does not require such hardware changes. One proposal is to map the 56-bit MEID to a 24-bit value, concatenate a fixed 8-bit value to the 24-bit mapped value and create a 32-bit pseudo-ESN. The pseudo-ESN could then be used as the ESN in the conventional public long code mask generation process.
However, it has been shown that this pseudo-ESN method does not result in a sufficient number of different public long code masks to prevent an undesirable number of collisions between mobile station communications. A collision occurs when the transmissions from two or more mobile stations 12 are not uniquely identifiable.
Other techniques have been proposed to resolve this collision problem, including one in which PLCMs are assigned based on the longitude and latitude value of the base station. In this base station-assigned PLCM proposal (hereinafter referred to as “BSAPLCM” proposal), all of the base stations use only one fixed format that supports all cell sizes, both large and small. In the BSAPLCM proposal, and as shown in
The BSAPLCM proposal suggests that a given base station can be identified to a precision of substantially 0.25 seconds if 22-bit and 23-bit values are used to respectively represent the latitude and the longitude information associated with that base station. However, using a combined 44-bit value to represent the latitude and longitude information is not feasible because of the restriction imposed by the 42-bit long PLCM value. The proposal suggests using, for example, 11 bits to represent the latitude value and 11 bits to represent the longitude value of a base station, as shown in
Reducing the longitude and latitude fields from the respective 23 and 22 bits to 11 bits naturally results in a loss of resolution in terms of the precision by which a particular base station can be distinguished from another at a given location. For example, according to the BSAPLCM proposal, shifting the higher-bit values by 5 bits results in a 0.15 mile granularity. That is, the base stations located within 0.15 miles of each other will have identical 11-bit longitude and latitude values. Thus, the base stations within this range cannot be distinguished from each other. Furthermore, the proposal acknowledges that reducing the number of bits employed to represent the longitude and latitude values exacerbates this issue, as two stations located 314 miles apart will have the same 11-bit longitude and latitude values. The proposal refers to the distance at which the base stations may have the same 11-bit longitude and latitude values repeat as the “reusable distance” (e.g., the 314 miles in the example discussed above).
The BSAPLCM proposal suggests that problems of multiple base stations that are located in close proximity (e.g., 0.15 miles) to each other, and thus have the same 11-bit longitude and latitude value, can be alleviated by partitioning the mobile station IDs (see
The BSAPLCM proposal suffers from at least one shortcoming in that its calculations for the reusable distance (e.g., ˜314 miles) are based upon conditions on or about the Earth's equator. That is, the proposal does not take into account the fact that the distance between longitudinal lines decrease as one moves away from the equator. As the distance between the longitudinal lines decrease, the reusable distance similarly decreases. A reduced reusable distance, however, is undesirable because the potential for collisions is greater. That is, as the reusable distance decreases, it becomes more likely that a mobile station 12 may obtain a PLCM in a first region and then travel the reusable distance to a second region where the same PLCM has been assigned to another mobile station 12. Accordingly, an improved way of generating PLCMs is desired to reduce the potential of collisions.
The present invention is directed to overcoming, or at least reducing, the effects of, one or more of the problems set forth above.
In one embodiment of the present invention, a method is provided. The method comprises defining a geographical position of a base station by a first coordinate value and a second coordinate value; modifying the first coordinate value based on the second coordinate value; and generating an identifier based on at least the modified first coordinate value.
In one embodiment of the present invention, an apparatus is provided for generating code masks that are associated with a base station that is definable by a latitudinal value and a longitudinal value. The apparatus comprises a storage unit having a plurality of code masks stored therein, wherein the code masks are generated by modifying the longitudinal value based on the latitudinal value. The apparatus further comprises a control unit communicatively coupled to the storage unit, the control unit adapted to assign at least one of the plurality of stored code masks to a mobile unit in response to detecting a call activation.
In one embodiment of the present invention, a system is provided. The system includes a mobile unit and a base station that is definable by a latitudinal value and a longitudinal value. The base station includes access to a plurality of code masks, wherein the code masks are generated by modifying the longitudinal value based on the latitudinal value, and wherein the base station is adapted to assign at least one of the plurality of the code masks to the mobile unit in response to detecting a call activation.
In one embodiment of the present invention, a method is provided. The method includes receiving a code mask associated with a base station that is definable by a latitudinal value and a longitudinal value, wherein the received code mask is generated by modifying the longitudinal value based on the latitudinal value. The method further comprises coding information using the received code mask.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
Turning now to the drawings, and specifically referring to
The communications system 100 of
In the communications system 100 of
The base stations 130, in the illustrated embodiment, include a code mask (CM) manager 160 that, as described in greater detail below, manages (e.g., creates, assigns, tracks) code masks. In the illustrated embodiment, the code mask manager 160 specifically manages public long code masks (PLCMs). The code mask manager 160 may be implemented in software, hardware, or a combination thereof.
In accordance with one or more embodiments of the present invention, an improved scheme is provided for determining and assigning PLCMs to facilitate communications with the mobile units 120 in a manner that reduces the potential for collisions. Although not so limited, for the purposes of this discussion, the PLCMs are generated in accordance with the format shown in
The communications system 100 also allows for soft and hard handovers. In instances when users change between different service networks, a hard handoff is required. In accordance with one embodiment of the present invention, a mobile unit 120 is assigned a new PLCM on a hard handoff, where the new PLCM will be based on the coordinates of the target base station 130. Assigning a new PLCM to the mobile station 120 on a hard handoff reduces the potential for collisions.
It should be understood that the configuration of the communications system 100 of
Referring now to
The generating module 430, described in greater detail in
The assigning and tracking module 440 of the base station 130 determines which PLCMs are available from the pool 450 and assigns one of the available PLCMs to a mobile unit 120 desiring to establish a connection. The assigning and tracking module 440 thus tracks the PLCMs that are in use, and can determine which PLCMs are available for use. In the illustrated communications system 100 of
Referring now to
As shown in
The generating module 430 determines (at 520) the longitude of the base station 130. This longitudinal value may be represented using, for example, a 23-bit value, and may be expressed in “y” seconds. In one embodiment, the longitude may be pre-stored in the base station, and, as such, the act of determining (at 505) the longitude may comprise retrieving the stored value. The generating module 430 determines (at 530) a value associated with the determined longitude based on the latitude of the base station 130. In one embodiment, the value associated with the longitude may be determined (at 530) by adjusting (at 532) the full 23-bit value of the longitude of the base station 130 by a preselected amount, wherein the preselected amount is determined by the latitude of the base station 130. The manner in which the longitudinal value of the base station 130 may be adjusted (at 532) is better understood with reference to
As noted previously, because the distance between the longitude lines decrease as one moves away from the equator, the reusable distance similarly decreases. A reduced reusable distance, however, is undesirable because the potential for collisions is greater.
In the example shown in
Referring again to
Based on at least the value associated with the longitude that is determined (at 530), the generating module 430 generates (at 540) a PLCM in accordance with the format shown in
It should be appreciated that the format shown in
At block 720, the base station 130 assigns the PLCM (determined at block 710) to the mobile unit 120. Assigning the PLCM to the mobile unit 120 may include informing the mobile station 120 of that PLCM. This can be accomplished in one of several ways. In one embodiment, the PLCM may be transmitted over a suitable communications channel to mobile unit 120, which then codes the transmission using the PLCM, and the base station 130 thereafter decodes the transmission using the PLCM. In an alternative embodiment, if the latitude and longitude of the base station 130, along with the MS ID, are accessible to the mobile unit 120, the mobile unit 120 itself can, using the method described in
Upon assigning the PLCM (at 720), the base station 130 may communicate with the mobile unit 120. That is, the base station 130 may decode (at 740) the information transmitted over a communications channel, such as a traffic channel, using the PLCM. And, once the call is terminated, the assigning and tracking module 440 releases (at 760) the PLCM assigned to the mobile unit 120 so that it can be later reused for another call.
Unless specifically stated otherwise, or as is apparent from the discussion, terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical, electronic quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system's memories or registers or other such information storage, transmission or display devices.
Those skilled in the art will appreciate that the various system layers, routines, or modules illustrated in the various embodiments herein may be executable control units (such as the control unit 410 (see
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
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|2||Higuchi, K. et al.: "Fast Cell Search Algorithm in DS-CDMA Mobile Radio Using Long Spreading Codes," Vehicular Technology Conference, 1997, IEEE 47th Phoenix, AZ, USA May 4-7, 1997, New York, NY, USA, IEEE, US May 4, 1997, pp. 1430-1434.|
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|U.S. Classification||455/456.1, 455/456.5|
|International Classification||H04W16/00, H04W24/00|
|Cooperative Classification||H04W16/00, H04W88/08|
|Aug 15, 2003||AS||Assignment|
Owner name: LUCENT TECHNOLOGIES INC., NEW JERSEY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:PATEL, SARVAR M.;REEL/FRAME:014405/0371
Effective date: 20030815
|Aug 10, 2009||AS||Assignment|
Owner name: ALCATEL-LUCENT USA INC., NEW JERSEY
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